The present invention is directed to an improved method and apparatus for chemically reacting liquids or slurries of liquids and solids with gasiform materials by the "ebullated bed process." The ebullated bed process generally comprises passing concurrently flowing streams of liquids or slurries of liquids and solids and gasiform materials through a generally cylindrical vessel which contains a mass of particulate contact material. The mass of contact particles is placed in random motion in the liquid medium, and has a gross volume dispersed through the liquid medium greater than the volume of the mass when stationary. This technology has found commercial application in the upgrading of heavy liquid hydrocarbons or converting coal to synthetic oils.
The process is generally described in U.S. Pat. No. Re 25,770 to Johanson, with particular reference to coal and oil conversion. A mixture of hydrocarbon liquid and hydrogen is passed upwardly through a bed of catalyst particles at a rate such that the particles are placed into random motion as the liquid and gas are passed upwardly through the bed, and the catalyst bed motion is controlled by a recycle liquid flow such that the majority of the catalyst particles do not rise above a certain level in the reactor. The liquid which is being hydrogenated along with the vapors present in the reaction pass through that upper level of catalyst particles and are removed from the upper portion of the reactor.
In the normal operation of such a system, there are substantial amounts of hydrogen gas and light hydrocarbon vapors which rise through the reaction zone into the liquid section from which the liquid is either recycled to the bottom of the reactor or forms liquid effluent. The presence of gases and vapors in the recycle stream present a separation problem, since a liquid portion recycled to the bottom of the reactor passes through a pump which must be carefully controlled in order to maintain the expansion and random motion catalyst particles at a constant and stable level. Any gases or vapors present in the recycled liquid materially decrease the capacity and efficiency of the recycle pump as well as the flow pattern and thus decrease the stability of the ebullated bed.
Typically, the reactors employed in catalytic hydrogenation processes using ebullated beds of catalyst particles are designed with a central vertical conduit which serves as the downcomer for recycling clear liquid from above the level of the ebullated catalyst bed to the suction of a recycle pump for recirculating the liquid through the catalytic reaction zone. The recycling of material from the upper portion of the reactor serves to ebullate the catalyst bed, maintain the temperature uniformly throughout the reactor, and stabilize the catalyst bed.
One prior art method for effective gas-liquid recycle is shown in U.S. Pat. No. 3,124,518 to Guzman, which discloses a downcomer fitted with a large entrance cone or funnel having a maximum cross-sectional area of approximately 1/2 that of the entire reaction zone. This permits the velocity of the liquid to slow relative to the gas, so the gas which is entrained in the liquid can have an opportunity to separate from the liquid and rise to the liquid-gas interface above the cup, prior to recycling the liquid.
Another prior art recycle device is disclosed in U.S. Pat. No. 3,227,528 to Jaeger which shows a recycle conduit similar to that of Guzman, except that it is connected to a pump.
Another reactor configuration for such gas-liquid separation is disclosed in U.S. Pat. No. 3,414,386 to Mattix, which discloses a reactor having a conical-shaped recycle device with its outer or upper end in peripheral contact with the reactor wall and conduits for the upflow of gas and liquid penetrating the device and extending above the reactor liquid level; a central conduit returns the liquid to the recycle pump. Also, the conduits through which liquids and gases pass are positioned such that the lower portion of the conduit for liquids extends into the liquid, whereas the conduit for gases is above the liquid interface. The upper ends of both conduits terminate in the vapor space of the reactor.
Experience has shown that this arrangement with the fluid conduits terminating above the liquid level does not provide effective separation and actually contributes to gas entrainment in the recycled liquid. Thus, there has been a distinct need for an improved means for quickly and efficiently separating gas from liquid being recycled in such a catalytic reaction step, so that the throughput and efficiency of the entire hydrogenation reaction process can be significantly increased.